Skylight type windows such as are installed in a roof, present a combination of problems, including aesthetic appeal, ease of installation, economy in manufacture, thermal insulation, and weatherproofing.
By far the most important factor however is the provision of a complete weather seal, preventing entry of moisture as a result of rain, snow, ice and the like.
Windows are available which satisfy one or some of these requirements, but generally speaking it has not been possible to achieve a satisfactory solution to all of these requirements in any one window.
Various different materials have been used in the past for such windows, with mixed results. Extrusion of a window frame in plastics material typically vinyl plastics material offers numerous advantages from the viewpoint of economy, and weather resistance. However, in the past vinyl extruded windows of this type have generally speaking been either excessively complex in design or else have provided an inadequate seal either between the roof and the window frame, or between the frame and the glazing.
Preferably the window frame consists of an essentially one-piece integral design, but it may be difficult to manufacture. In this case it may be advantageous if the window frame is a two-part design, consisting of a window base and flashing, and a window housing attached to the window base.